Hydrogen photoproduction by immobilized S-deprived Chlamydomonas reinhardtii: Effect of light intensity and spectrum, and initial medium pH

Sulfur deprivation creates anaerobic conditions and thereby induces hydrogen photoproduction by the green microalga Chlamydomonas reinhardtii. In the present work we showed that immobilization of C. reinhardtii within a thin Ca-alginate film extended the duration of hydrogen evolution under sulfur depletion up to three weeks with hydrogen production limited mainly by exhaustion of intracellular starch reserves. The optimal incident light intensity for hydrogen photoproduction appeared to be about 80 μmol photons m− 2 s− 1 at which the total amount of evolved hydrogen reached 0.8 mmol per mg chlorophyll. Illumination by monochromatic blue light peaking at 435 nm or red light with maximum at 690 nm, both favoring PSI excitation, improved the stability of PSII centers and enhanced hydrogen evolution. Initial medium pH in the range 6.5-7.0 was optimal for hydrogen photoproduction, likely due to enhanced accumulation of starch and elevated initial PSII activity.